A physically based description for coupled plasticity and creep deformation

Based on a simple mechanical model and an appropriate definition of generalized time, a constitutive equation without using a yield surface is obtained for coupled plasticity and creep behavior of materials. The hardening of the materials is separated into two factors related respectively to inelastic strain range and nonproportionality. The steady creep of aluminum, copper and nickel under wide variation of equivalent stress, and the coupled plasticity and creep of 304 stainless steel subjected to non-steady slate of biaxial stress at elevated temperature are analyzed. The validity of the proposed model is demonstrated by the satisfactory agreement between the experimental and calculated results. Since the proposed model does not use a yield surface, the corresponding numerical analysis for coupled plasticity and creep becomes greatly convenient. (C) 1998 Elsevier Science Ltd. All rights reserved.